Type alias VTTScrollSetting

VTTScrollSetting: "" | "up"

A WebVTT-defined region scroll setting, represented by a value from the following list:
- '': None. Cues in the region stay fixed at the location they were first painted in.
- 'up': Up. Cues in the region will be added at the bottom of the region and push any already displayed cues in the region up until all lines of the new cue are visible in the region.